Rotor cores for use in electric motors, for example, have a ring shape (hollow cylindrical shape) constructed from a stack of thin steel sheets. Each of the thin steel sheets is cut from a steel sheet into a ring shape. Scrap metal cut off from inside the ring sheet is wasted.
In an attempt to utilize the steel sheet at an increased rate, a rotor core is known, which comprises a plurality of separate core plates in the form of circumferentially separate sectorial thin steel sheets.
The present applicant has proposed a method of manufacturing a rotor core (ring core) by alternately stacking and forming separate core plates, as disclosed in Patent Document 1. According to this proposed manufacturing method, it is possible to increase the rate of utilization of the sheet material, and shorten the time required to stack the separate core plates.
When separate core plates are stacked to produce a ring core, it is desirable to further shorten the time required to stack the separate core plates, as well as to stack the separate core plates with higher accuracy.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2006-223022